Apilimod, also referred to as STA-5326, hereinafter “apilimod”, is recognized as a potent transcriptional inhibitor of IL-12 and IL-23. See e.g., Wada et al. Blood 109 (2007): 1156-1164. IL-12 and IL-23 are inflammatory cytokines normally produced by immune cells, such as B-cells and macrophages, in response to antigenic stimulation. Autoimmune disorders and other disorders characterized by chronic inflammation are characterized in part by inappropriate production of these cytokines. In immune cells, the selective inhibition of IL-12/IL-23 transcription by apilimod was recently shown to be mediated by apilimod's direct binding to phosphatidylinositol-3-phosphate 5-kinase (PIKfyve). See, e.g., Cai et al. Chemistry and Biol. 20 (2013):912-921. PIKfyve plays a role in Toll-like receptor signaling, which is important in innate immunity.
Based upon its activity as an immunomodulatory agent and a specific inhibitor of IL-12/IL-23, apilimod has been proposed as useful in treating autoimmune and inflammatory diseases and disorders. See e.g., U.S. Pat. Nos. 6,858,606 and 6,660,733 (describing a family of pyrimidine compounds, including apilimod, purportedly useful for treating diseases and disorders characterized by IL-12 or IL-23 overproduction, such as rheumatoid arthritis, sepsis, Crohn's disease, multiple sclerosis, psoriasis, or insulin dependent diabetes mellitus). Similarly, apilimod was suggested to be useful for treating certain cancers based upon its activity to inhibit c-Rel or IL-12/23, particularly in cancers where these cytokines were believed to play a role in promoting aberrant cell proliferation role. See e.g., WO 2006/128129 and Baird et al., Frontiers in Oncology 3:1 (2013, respectively).
Each of three clinical trials of apilimod has focused on its potential efficacy in autoimmune and inflammatory diseases. The trials were conducted in patients having psoriasis, rheumatoid arthritis, and Crohn's disease. An open label clinical study in patients with psoriasis concluded that oral administration of apilimod showed immunomodulatory activity supporting the inhibition of IL-12/IL-23 synthesis for the treatment of TH1- and TH17-mediated inflammatory diseases. Wada et al., PLosOne 7:e35069 (April 2012). But the results of controlled trials in rheumatoid arthritis and Crohn's disease did not support the notion that IL-12/IL-23 inhibition by apilimod translates into clinical improvement in either of these indications. In a randomized, double-blind, placebo-controlled Phase II clinical trial of apilimod in patients with rheumatoid arthritis, apilimod failed to alter synovial IL-12 and IL-23 expression. Krauz et al., Arthritis & Rheumatism 64:1750-1755 (2012). The authors concluded that the “results do not support the notion the IL-12/IL-23 inhibition by apilimod is able to induce robust clinical improvement in RA.” Similarly, a randomized, double-blind, placebo-controlled trial of apilimod for treatment of active Crohn's disease concluded that, although well tolerated, apilimod did not demonstrate efficacy over placebo. Sands et al Inflamm Bowel Dis. 2010 July; 16(7):1209-18.
The mammalian target of rapamycin (mTOR) pathway is an important cellular signaling pathway that is involved in multiple physiological functions, including cell growth, cell proliferation, metabolism, protein synthesis, and autophagy (La Plante et al Cell 2012, (149 (2), pp. 274-293). mTOR is a kinase that integrates intracellular and extracellular cues that signal the levels of amino acids, stress, oxygen, energy, and growth factors and regulates the cellular response to these environment cues. mTOR deregulation has been implicated in a wide range of disorders and diseases, including cancer, obesity, diabetes, and neurodegeneration. Certain components of the mTOR pathway have been explored as drug targets for treating some of these diseases. However, therapeutic efficacy has been limited, for example, in the treatment of some cancers, and some mTOR inhibitors have been shown to have an adverse effect on metabolism. The tuberous sclerosis complex tumor suppressor genes, TSC1 and TSC2, are negative regulators of mTOR.